Compact, portable resistance heating device

ABSTRACT

A compact, portable resistance heating device that takes a source of alternating current electricity and through a series of connections and circuitry splits the alternating current electricity into a plurality of circuits. The compact, portable resistance heating device is capable of heating a plurality of cartridge heaters at one time, individually or a combination thereof. The compact, portable resistance heating device is controlled by at least one controller that controls three (3) power output receptacles. The controller is capable of producing 0-100% output power to each respective cartridge heater. Each cartridge heater may be individually controlled by an on/off switch, and an indicator light may be provided and illuminate when each cartridge heater is energized. The cartridge heaters of the compact, portable resistance heating device do not require close tolerances with an axial bore of a stud or threaded bolt and are further capable of being bent to suit the particular operation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/113,513, filed May 1, 2008, which claims the benefit of U.S.Provisional Application Ser. No. 60/927,509, filed on May 4, 2007, eachof which is incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTINGAPPENDIX

Not Applicable.

STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINTINVENTOR

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a compact, portable resistanceheating device, and more particularly to a compact, portable resistanceheating device for heating and stretching a rod or post, such as a studor threaded bolt, on a steam turbine casing, a heat exchanger, or thelike.

2. Description of the Related Art

Commonly, a bolt heater is used to fasten or loosen a bolt or stud usedon steam turbine casings or the like that cannot be fastened or loosenedby a wrench or spanner whereby the bolt heater raises the temperature ofthe bolt or stud by subjecting it to an alternating current electricity.The alternating current flowing from the bolt heater induces eddycurrents in the bolt or stud and the resistance leads to Joule heatingcausing the bolt or stud to be become heated and stretch or elongate.Typically, the depth to which the eddy currents penetrate, and thereforethe distribution of heat within the bolt or stud, depends on thefrequency of the alternating current and the magnetic permeability, aswell as the resistivity, of the bolt or stud. During this process, thebolt or stud will elongate or stretch due to expansion during heating,thereby allowing a nut to be threaded onto the bolt or stud to a greaterdegree during the fastening operation. As the bolt or stud cools andshrinks, the nut is pulled tautly against the surrounding surface of theturbine casing or heat exchanger. This process ensures a secure and firmconnection of the nut on the bolt.

For removal of a bolt or stud, such as during servicing of the turbineor heat exchanger, the reverse process is followed. The bolt or stud isheated causing it to stretch, and in so doing, the nut moves away fromthe surrounding surface and lessens the force holding the nut againstthe surrounding surface of the turbine casing or heat exchanger.

Known resistance type bolt heaters operate at 240 volts or 480 volt,three-phase alternating current. Typically, these known bolt heaters areindividually controlled and require five minutes or more to sufficientlyheat and stretch each bolt for fastening or removal. In addition, theseknown resistance type bolt heaters require close tolerances between theaxial bore of the bolt or stud and bolt heater. Further, the poweroutput of these known resistance type bolt heaters cannot be varied andthe bolt heaters cannot be removed from the bolt prior to cooling. Ifthese known resistance type bolt heaters are removed from the bolt priorto cooling, the bolt heater will overheat and burn out because theproduced heat is not dissipated. Furthermore, these known resistancetype bolt heaters are not capable of being bent or shaped to fit theuser's particular need.

A major limitation of these current brain stimulation therapies,however, is that they are all administered without regard to thenatural, continuous, and ongoing fluctuations in the activity of apatient's brain.

It is therefore desirable to provide a compact, portable resistanceheating device capable of heating and stretching a plurality of bolts orstuds simultaneously regardless of the diameter of the bolt or stud.

It is further desirable to provide a compact, portable resistanceheating device capable of heating and stretching a plurality of bolts orstuds that do not have an axial bore or that have an axial bore eitherindividually, in totality or a combination thereof.

It is still further desirable to provide a compact, portable resistanceheating device that is sufficiently portable, compact and lightweight soas to be easily movable by a single user on a turbine deck, a deck of anoil refinery or the like.

It is yet further desirable to provide a compact, portable resistanceheating device that does not require a cooling fluid, hydraulic pumps orair hammers during operation.

It is yet further desirable to provide a compact, portable resistanceheating device having a selectively variable output power range from 0to 100%.

It is yet further desirable to provide a compact, portable resistanceheating device that utilizes a cartridge heater having a heating elementthat is not limited by clearance between the axial bore of the bolt orstud and the heating element.

It is yet further desirable to provide a compact, portable resistanceheating device that utilizes a cartridge heater having a heating elementthat is capable of being bent or shaped.

It is yet further desirable to provide a compact, portable resistanceheating device having a plurality of cartridge heaters that are capableof operation either individually or a combination thereof.

It is yet further desirable to provide a compact, portable resistanceheating device capable of heating and stretching a bolt or stud in underfive minutes time.

It is yet further desirable to provide a compact, portable resistanceheating device that reduces man hours and outage times.

SUMMARY OF THE INVENTION

In general, in a first aspect, the invention relates to a compact,portable resistance heating device. The device includes a compact,portable housing configured to be connected to a source of three-phasealternating current electricity, with the three-phase alternatingcurrent electricity being split into separate legs of single-phasealternating current electricity. A step-down transformer is configuredto power a controller, and the controller is configured to control aplurality of receptacles. The receptacles are connected to the housingand configured to receive the single-phase alternating currentelectricity. The controller is configured to selectively output thesingle-phase alternating current electricity to each of the receptacles.

The three-phase alternating current electricity may be 480 voltthree-phase alternating current electricity, and the single-phasealternating current electricity may be 480 volt single-phase alternatingcurrent electricity. The transformer is not required to provide voltagerecognition and may balance the electric output of each of thereceptacles based on the number of powered cartridge heaters. Thesingle-phase alternating current electricity can be varied from 0 to100% using the controller, and for powering cartridge heaters eitherindividually or in a combination thereof.

The housing of the compact, portable resistance heating device mayfurther include an indicator lamp and an on/off switch associated witheach of the receptacles. The on/off switch associated with each of thereceptacles enables a user to selectively control an electric output ofeach of the receptacles.

The compact, portable resistance heating device for stretching a boltmay also include a plurality of cartridge heaters, wherein each of thecartridge heaters includes a cartridge heater cable at one endterminating with a plug configured to be received in one of thereceptacles and having a heating element at an opposite end. Each of thecartridge heaters does not require close tolerances between the heatingelement and a bore of the bolt. Moreover, the heating element of each ofthe cartridge heaters may be bent, shaped or coiled. An on/off switchassociated with each of the receptacles enables a user to selectivelycontrol an electric output of each of the receptacles, while each of thetransformers balances the electric output to each of the receptaclesbased on the number of active receptacles.

The heating element of each of the cartridge heaters can further includea heating rod and a dielectric insulator sheathed within an outercasing. The dielectric insulator can be a dielectric fluid. Each of thecartridge heaters may be capable of providing high voltage, high wattageand low amperage, namely wattage of up to approximately 2000 watts andamperage between approximately 4 and approximately 30 amps.

In general, in a second aspect, the invention relates to a cartridgeheater for a resistance heating device. The cartridge heater includes acartridge heater cable at one end terminating with a plug configured tobe received in a receptacle and having a heating element at an oppositeend. The heating element has an internal thermal conducting materialsurrounded by an intermediate layer of a dielectric insulator sheathedwithin an outer casing. The cartridge heater is configured to provide awattage of up to approximately 2000 watts and an amperage betweenapproximately 4 and approximately 30 amps.

The heating element may be bent, shaped or coiled. In addition, thedielectric insulator can be a dielectric fluid, such as a ferrous metal,namely nickel or chromium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example of a compact, portableresistance heating device in accordance with an illustrative embodimentof the compact, portable resistance heating device disclosed herein;

FIG. 2 is a partial cutaway perspective view an example of a cartridgeheater of the compact, portable resistance heating device in accordancewith an illustrative embodiment of the compact, portable resistanceheating device disclosed herein;

FIG. 3 is a perspective view of another example of a cartridge heater ofthe compact, portable resistance heating device in accordance with anillustrative embodiment of the compact, portable resistance heatingdevice disclosed herein; and

FIG. 4 is an electrical schematic of the compact, portable resistanceheating device in accordance with an illustrative embodiment of thecompact, portable resistance heating device disclosed herein.

Other advantages and features will be apparent from the followingdescription and from the claims.

DETAILED DESCRIPTION OF THE INVENTION

The devices and methods discussed herein are merely illustrative ofspecific manners in which to make and use this invention and are not tobe interpreted as limiting in scope.

While the invention has been described with a certain degree ofparticularity, it is to be noted that many modifications may be made inthe details of the construction and the arrangement of the elements andcomponents of the devices and/or in the sequences and steps of themethods without departing from the scope of this disclosure. It isunderstood that the devices and methods are not limited to theembodiments set forth herein for purposes of exemplification.

The description of the invention is intended to be read in connectionwith the accompanying drawings, which are to be considered part of theentire written description of this invention. In the description,relative terms such as “front,” “rear,” “lower,” “upper,” “horizontal,”“vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as wellas derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,”etc.) should be construed to refer to the orientation as then describedor as shown in the drawings under discussion. These relative terms arefor convenience of description and do not require that the machine beconstructed or the method to be operated in a particular orientation.Terms, such as “connected,” “connecting,” “attached,” “attaching,”“join” and “joining” are used interchangeably and refer to one structureor surface being secured to another structure or surface or integrallyfabricated in one piece.

Referring to the figures of the drawings, wherein like numerals ofreference designate like elements throughout the several views, andinitially to FIG. 1, a compact, portable resistance heating device 10that may be used in a wide variety of environments, such as for heatingand stretching studs or bolts of turbine casings in power plants or ofheat exchangers in oil refineries. The compact, portable resistanceheating device 10 should not be so limited to such environments, but israther described with reference to such environments for exemplificationpurposes only.

As illustrated in FIG. 1, the compact, portable resistance heatingdevice 10 includes a compact housing 12 capable of being easily movedfrom one location to another, such as on a plurality of wheels orcasters 14. The compact housing 12 may be approximately 170 pounds(77.1107029 kilograms) and may be approximately two (2) feet (0.6096meters) wide, two (2) feet (0.6096 meters) deep and two and one-half(2½) feet (0.762 meters) tall, thus allowing the compact housing 12 tobe easily movable by a single user on a turbine deck or on a deck of anoil refinery. The compact housing 12 may include a junction box 16 forconnection of a source of alternating current electricity 18, such as480 volt, 60 amp three-phase alternating current electricity, from anexternal power source, such as deck power or by generator. The source ofalternating current electricity 18 may be brought into the housing 12and connected to a junction terminal block (not shown) secured withinthe junction box 16.

The housing 12 also includes a plurality of receptacles 20. Each of thereceptacles 20 may include a corresponding indicator light 22 and on/offswitch 24. Each indicator light 22 may be located adjacent to therespective receptacle 20 so as to alert the user that the receptacle isenergized and ready for use. Also located adjacent to each receptacle 20may be the respective on/off switch 24 allowing the user to selectivelyturn on or off the respective receptacle 20. Each receptacle 20 isconfigured to receive and be connected with a plug 26 on a terminal endof a cartridge heater cable 28 of a cartridge heater 30.

The housing 12 also includes components and circuitry for heating andstretching a rod or post, such as a stud or threaded bolt, on a steamturbine casing, a heat exchanger, or the like. The components andcircuitry for the compact, portable resistance heating device 10 may bemounted to an interior portion of the housing 12. The compact, portableresistance heating device 10 includes at least one controller 32connected to the source of alternating current electricity 18 forcontrolling at least one transformer 34, as fully discussed below withreference to FIG. 4. The controller 32 and transformer 34 control andpower a plurality of the receptacles 20. The compact, portableresistance heating device 10 may also include a fan 56, a circuitbreaker 52, fuses 62, fuse blocks 68, terminal blocks 58 and 64 andwiring arranged to deliver the source of alternating current electricity18 through the controller 32 and transformer 34 to the plurality ofreceptacles 20 on the housing 12.

FIGS. 2 and 3 illustrate two examples of a cartridge heater 30 of thecompact, portable resistance heating device 10, wherein each cartridgeheater 30 includes the plug 26 on a terminal end of the cartridge heatercable 28. The plug 26 of the cartridge heater 30 is configured toreceive and be connected to a receptacle 20 on the housing 12 of thecompact, portable resistance heating device 10. The cartridge heater 30also includes a heating element 36 connected to the cartridge heatercable 28 via a cartridge heater junction box 38. The cartridge heaterjunction box 38 may include a handle 40 to allow the user to hold andoperate the cartridge heater 30. The heating element 36 of the cartridgeheater 30 includes an internal heating rod 42 and a dielectric insulator44 sheathed within an outer casing 46. The internal heating rod 42 isconstructed of a thermal conducting material, such as a ferrous metal,for example nickel or chromium, whereas the dielectric insulator 44 maybe a dielectric fluid. As illustrated in FIG. 2, the heating element 36of the cartridge heater 30 is cylindrical and sized to be inserted intoan axial hole or bore in a bolt or stud to heat and stretch the bolt fortightening or loosening. Because the cartridge heater 30 includes thedielectric insulator 44, the heating element 36 does not require closetolerances with the bore of the bolt or stud, which is of a benefitsince the axial bore diameter of bolts or stud can and do vary for aparticular job. By not requiring close tolerances between the heatingelement 36 and the bore, the presence of burrs or spurs within the axialbore of the bolt or stud does not pose any difficulties and allows theuser to utilize any sized cartridge heater 30 for any job.

Further, the design of the cartridge heater 30 dramatically increasesthe life cycle of the cartridge heater 30. Because of this increasedlife cycle, the cartridge heater 30 may be reused in subsequentoperations and is not required to be changed out during a particularjob. In addition, the cartridge heater 30 of the compact, portableresistance heating device 10 utilizes 480 volt single-phase alternatingcurrent electricity provided and controlled by the controller 32 andtransformer 34. The cartridge heater 30 may further utilize high wattageand low amperage, such as 2000 watts and 4 to 30 amps. Furthermore, thecartridge heaters 30 of the compact, portable resistance heating device10 may be removed from the bore of the stud or bolt prior to beingde-energized without the cartridge heater 30 overheating. The heatingelement 36 of the cartridge heater 30 also is capable of being bent orshaped to suit a particular job. Given the ability of heating element 36of the cartridge heater 30 to be bent, the compact, portable resistanceheating device 10 may be used on bolts or studs without an axial bore,such as on heat exchangers in oil refineries. As shown in FIG. 3, theheating element 36 of the cartridge heater 30 may be coiled around theouter diameter of the head 48 of a bolt or stud 50 for heating andstretching the bolt or stud during installation or removal operations.

During installation, the heating element 36 of the cartridge heater 30is inserted into the axial bore of a stud or bolt without requiringclose tolerances between the heating element 36 and the bore, or if thestud or bolt does not have an axial bore, the heating element 36 of thecartridge heater 30 is coiled around the head 48 of the stud or bolt 50.The cartridge heater 30 is energized with single-phase alternatingcurrent electricity by the user and the heating element 36 increases thetemperature of the stud or bolt, causing it to stretch longitudinally. Athreaded nut is then tightened onto the stud or bolt and the heatingelement 36 of the cartridge heater 30 is removed, allowing the stud orbolt to cool and shrink, thereby increasing the holding force of the nuton the stud or bolt. During removal of the nut from the stud or bolt,the reverse process is employed.

FIG. 4 illustrates a schematic diagram of the compact, portableresistance heating device 10. As previously discussed, the source ofthree-phase alternating current electricity 18, such as 480 voltthree-phase alternating current electricity, is connected to thejunction terminal block secured within the junction box 16 of thehousing 12 of the compact, portable resistance heating device 10. Asshown in FIG. 4, the source of alternating current electricity 18 maysupply power through three power lines L1 (black), L2 (white) and L3(red) and a ground wire (G). The source of alternating currentelectricity 18 may be brought from the junction terminal block in thejunction box 16 to a main breaker 52. The main breaker 52 may be a 480volt/100 amp breaker. From the main breaker 52, two (2) phases of thethree-phase alternating current electricity may be carried to astep-down transformer 54, such as a 480 volt/110 volt step-downtransformer, to power a controller 32, a fan 56 and/or a transformer 34.For purposes of exemplification and as shown in FIG. 4, the step-downtransformer 54 may power a plurality of controllers 32 a and 32 b, witheach controller 32 a and 32 b controlling a respective transformer 34 aand 34 b. However, in keeping with the spirit and scope of the compact,portable resistance heating device 10, one skilled in the art willappreciate that the compact, portable resistance heating device 10 mayutilize a single controller 32 a to control a single transformer 34 a,which in turn may power a plurality of circuits for providing power tothe plurality of receptacles 20, as fully discussed below. Further, oneskilled in the art will appreciate that additional controllers andtransformers may be implemented to power and control additional circuitsand additional receptacles.

The three-phase alternating current electricity 18 from the main breaker52 may be connected in series with a first terminal block 58 along linesL1, L2 and L3. The first terminal block 58 may be secured to the housing12 using bolts and locking nuts. When a plurality of controllers 32 aand 32 b and transformers 34 a and 34 b are implemented, the firstterminal block 58 splits each phase of the three-phase alternatingcurrent electricity 18 across lines L1, L2, and L3 into two legs 60 aand 60 b, with each leg to run three (3) circuits of three (3)receptacles 20 each. From the first terminal block 58, two of thephases, which are now split, may be carried inline to fuses 62 a and 62b by lines L1 and L3. The fuses 62 a and 62 b may be FWP-40 amp fusesmounted on a DIN rail. The fuses 62 a and 62 b may be provided inline sothat they will burn out before any potential spikes in power are harmfulto either the user or the transformer(s) 34 a or 34 b. Only two (2) ofthe three (3) phases (L1 and L3) are required to be inline with thefuses 62 a and 62 b, while one (1) of the phases (L2) need not passthrough a fuse.

Once the three-phase alternating current electricity 18 has been splitinto two (2) legs 60 a and 60 b by the first terminal block 58 and twoof the phases carried by lines L1 and L3 are passed through fuses 62 aand 62 b, each leg is carried to a respective transformer 34 a and 34 b.Each transformer 34 a and 34 b balances the load of the respective leg60 a and 60 b of alternating current electricity 18 and provides novoltage recognition. Each transformer 34 a and 34 b recognizes the powerdraw based on the number of cartridge heaters 30 used, and therebyproviding multiple, adjustable voltage to each cartridge heater 30. Eachtransformer 34 a and 34 b converts the respective leg 60 a and 60 b ofthe three-phase alternating current electricity 18 to single-phasealternating current electricity for powering the cartridge heaters 30.Each transformer 34 a and 34 b is powered and controlled by therespective controller 32 a and 32 b, such as with 24 volts. Aspreviously described, each controller 32 a and 32 b is powered by thestep-down transformer 54 with 110 volts alternating current. Further,each controller 32 a and 32 b is capable of 0-100% power output to therespective transformer 34 a and 34 b. Each of the controllers 32 a and32 b control the power output to three (3) receptacles 20. Each or bothof the controllers 32 a and 32 b may also include a thermocouple tomonitor the ambient temperature within the housing 12 of the compact,portable resistance heating device 10. The step-down transformer 54 mayalso be used to power a fan 56 to keep the transformer 34 a/34 b coolduring operation.

Once three-phase alternating current electricity 18 is passed through atransformer 34 a and/or 34 b, the single-phase alternating currentelectricity may be carried by lines L1, L2 and L3 to a second terminalblock 64. Again for purposes of exemplification and as shown in FIG. 4,the compact, portable resistance heating device 10 may utilize aplurality of transformers 34 a and 34 b, and in such a case, thesingle-phase alternating current electricity is passed from therespective transformer 34 a/34 b to a respective second terminal block64 a/64 b. Each of the second terminal blocks 64 a/64 b split thesingle-phase alternating current electricity into two sets of six leads66 a through 66 e, which is then passed to a fuse block 68 a/68 b toform three (3) circuits, wherein leads 66 a and 66 b form one circuit,leads 66 c and 66 d form a second circuit, and leads 66 e and 66 f forma third circuit. Each fuse block 68 a and 68 b may include six (6)fuses, such as KTK-15 or KTK-30 amp fuses, mounted on a DIN rail. Eachcircuit may comprise a receptacle 20, an indicator light 22 and anon/off switch 24. Each circuit is controlled by the respectivecontroller 32 a/32 b and powered by the respective transformer 34 a/34b. Each circuit is powered and fed through the fuse block 68 a/68 b.Main circuit power wires 70 a and 70 b, 70 c and 70 d, and 70 e and 70 fare routed to one of the on/off switches 24. The on/off switches 24 maybe double pole, double throw (“DLDT”) switches. The first terminationpoint after the fuse block 68 a/68 b may be the bottom of the respectiveon/off switch 24. One of the main circuit power wires 70 a/70 c/70 e maycome out of the top of the on/off switch 24 to the bottom of theindicator light 22, while the other main circuit power wire 70 b/70 d/70f may come out of the top of the on/off switch 24 to the top of theindicator light 22. From the top of the indicator light 22 to the lasttermination point, the receptacle 20, one of the main circuit powerwires 70 a/70 c/70 e may go to one side of the receptacle 20 while theother main circuit power wire 70 b/70 d/70 f may go to the other side ofthe receptacle 20. When the plug 26 on the terminal end of theconducting cable 28 of the cartridge heater 30 is connected to arespective receptacle 20, the circuit is complete causing the heatingelement 36 to energize instantaneously with single-phase alternatingcurrent electricity.

Whereas, the devices and methods have been described in relation to thedrawings and claims, it should be understood that other and furthermodifications, apart from those shown or suggested herein, may be madewithin the scope of this invention.

What is claimed is:
 1. A compact, portable resistance heating device,comprising: a compact, portable housing configured to be connected to asource of three-phase alternating current electricity; said deviceconfigured to split said three-phase alternating current electricityinto separate legs of single-phase alternating current electricity; anda step-down transformer configured to power a controller; saidtransformer configured to provide no voltage recognition; saidcontroller configured to control a plurality of receptacles; saidreceptacles connected to said housing and configured to receive saidsingle-phase alternating current electricity; said controller configuredto selectively output said single-phase alternating current electricityto each of said receptacles; and said controller configured to balancesaid electric output of each of said receptacles based on a number ofpowered cartridge heaters.
 2. The compact, portable resistance heatingdevice of claim 1 wherein said three-phase alternating currentelectricity is 480 volt three-phase alternating current electricity. 3.The compact, portable resistance heating device of claim 1 wherein saidoutput of said single-phase alternating current electricity is 480 voltsingle-phase alternating current electricity.
 4. The compact, portableresistance heating device of claim 1 wherein each of said cartridgeheaters are configured to be powered individually or in a combinationthereof.
 5. The compact, portable resistance heating device of claim 1wherein said housing further includes an indicator lamp and an on/offswitch associated with each of said receptacles.
 6. The compact,portable resistance heating device of claim 5 wherein said on/off switchassociated with each of said receptacles enables a user to selectivelycontrol an electric output of each of said receptacles.
 7. The compact,portable resistance heating device of claim 1 wherein said controller iscapable of varying said output of said single-phase alternating currentelectricity between 0% and 100%.
 8. The compact, portable resistanceheating device of claim 7 wherein said controller comprises a pluralityof controllers electrically connected to said step-down transformer. 9.The compact, portable resistance heating device of claim 7 furthercomprising a plurality of circuits for respectively providing saidsingle-phase alternating current electricity to a plurality ofreceptacles.
 10. The compact, portable resistance heating device ofclaim 1 wherein said housing further includes an external junction boxfor connection of said source of three-phase alternating currentelectricity.
 11. The compact, portable resistance heating device ofclaim 1 further comprising a circuit breaker arranged to deliver saidsource of three-phase alternating current electricity through saidcontroller and said transformer to said plurality of receptacles. 12.The compact, portable resistance heating device of claim 1 furthercomprising a plurality of cartridge heaters configured to respectivelyoutput said single-phase alternating current electricity from saidreceptacles; wherein each of said cartridge heaters includes a cartridgeheater cable at one end terminating with a plug configured to bereceived in one of said receptacles and having a heating element at anopposite end.
 13. The compact, portable resistance heating device ofclaim 12 wherein said heating element of each of said cartridge heaterscomprising an internal heating rod constructed of a thermal conductingmaterial surrounded by a dielectric fluid insulator sheathed within anouter casing.
 14. The compact, portable resistance heating device ofclaim 13 wherein each of said cartridge heaters provides wattage of upto approximately 2000 watts and amperage between approximately 4 andapproximately 30 amps.